Variable amplitude polarizing beam splitter

ABSTRACT

A birefringence polarizer divides incident light into two emergent, mutually perpendicularly polarized beams. The incident light is linearly polarized, its azimuth of polarization being rotatable by a rotatable half-wave retardation plate. A similar plate in the path of one of the emergent beams controls its azimuth of polarization. The emergent light beams are thus controllable as to relative intensity and directions of polarization.

United States Patent Smith [54] VARIABLE AMPLITUDE POLARIZING BEAMSPLITTER [72] Inventor: Luther W. Smith, Brimfield, Mass.

[73] Assignee: American Optical Corporation, Southbridge, Mass.

22 Filed: May 19,1971

21 Appl. No.: 144,922

[52] U.S. Cl. ..350/157, 350/147, 350/159 [51] Int. Cl ..G02f 1/24 [58]Field of Search ..350/l50, 157, 159, DIG. 2,

[56] References Cited UNITED STATES PATENTS 7/1970 Leib et al. ..350/l5912/1969 Turner ..350/159 9/1968 Drougard et al. ..350/159 [451 Dec. 5,1972 OTHER PUBLICATIONS Horton, Conical Refraction Scanner" IBM Tech.Discl. Bull. Vol. 6, No. 12 (May 196 PP- 57-58 Primary Examiner-DavidSchonberg Assistant Examiner-Paul R. Miller Attorney-William C. Nealon,Robert J. Bird and Bernard L. Sweeney ABSTRACT A birefringence polarizerdivides incident light into two emergent, mutually perpendicularlypolarized beams. The incident light is linearly polarized, its azimuthof polarization being rotatable by a rotatable half-wave retardationplate. A similar plate in the path of one of the emergent beams controlsits azimuth of polarization. The emergent light beams are thuscontrollable as to relative intensity and directions of polarization,

4 Claims, 2 Drawing Figures PATENTEDBEB 5 I912 3.704.997

INVENTOR Lufher W Smith By fin)? W A forney VARIABLE AMPLITUDEPOLARIZING BEAM SPLITTER BACKGROUND OF THE INVENTION The presentinvention relates to a light beam splitter, and in particular to a beamsplitter providing variable amplitude and polarization of the lightbeams emerging therefrom.

One environment in which this invention might find application is in thefield of holography. In holography, beam splitters are used to producetwo mutually coherent emergent light beams from a single incident lightbeam. The relative intensities of the two emergent beams are fixed bythe characteristic of the beam splitter. That is, beam splitters knownto the prior art are capable of reflecting and transmitting in a certaincharacteristic ratio. It is desirable, to provide greater flexibility ina holographic apparatus, to provide different ratios of intensity of thetwo emergent beams (object and reference beams) from the beam splitter.An application of this invention to holography is described inapplicants copending application, Ser. No. 144,762 filed concurrentlyherewith.

SUMMARY OF THE INVENTION It is an object of this invention to provide abeam splitter in which the intensities of the emergent beams arevariable.

It is another object of this invention to provide a beam splitter inwhich the planes of vibration of the emergent linearly polarized beamsare variable.

Briefly, the present invention is practiced in one form by birefringencepolarizer disposed in the path of linearly polarized incident light. Thebirefringence polarizer divides the incident beam into two mutuallyperpendicularly polarized emergent beams. A halfwave retardation platein the path of the incident light is rotatable to vary the azimuth ofpolarization of the light incident on the birefringence polarizer. Therelative intensities of the emergent beams are thus controllable. Ahalf-wave plate in the path of one of the emergent beams controlsitsazimuth of polarization and in turn the relative directions ofpolarization of the two emergent beams.

DRAWING Other objects, advantages and features of this invention maybecome apparent from the following description taken in connection withthe accompanying drawmg.

FIG. I is an optical diagram of a beam splitter according to thisinvention;

FIG. 2 is an optical diagram of a holographic apparatus employing thebeam splitter of this invention, shown within the dotted line portion ofthe figure.

DESCRIPTION Referring now to FIG. 1, a birefringence polarizer isgenerally shown at 2 and is disposed, with a half-wave retardation plate4 along an optical axis 6. Birefringence polarizer 2 may be any one ofseveral known types including the Wollaston, Rochon, and Nicol prisms.The one illustrated in FIG. 1 is a Wollaston prism including segments 21and 22 joined at interface 23. The optic axes of segments 21 and 22 arein the directions illustrated by the lines and are mutuallyperpendicular. Birefringence polarizer 2 and half-wave plate 4 aremounted so as to be rotatable about axis 6.

Linearly polarized light, represented by the arrows 8, is directed alongaxis 6, through half-wave plate 4, onto the birefringence polarizer 2.The azimuth of polarization of incident light 8 is rotatable by rotationof the half-wave plate about axis 6, as represented by the arcuate arrowA. The birefringence polarizer 2 effects the splitting of incident beam8 into two mutually perpendicularly polarized emergent beams 10 and 12.The relative intensities of emergent beams 10 and 12 depend on theazimuth of polarization of incident light 8 as it strikes thebirefringence beam splitter 2. Beam splitter 2 is also mounted forrotation about axis 6 as indicated by arcuate arrow B.

A half-wave retardation plate 14 is disposed in the path of one of theemergent beams, for example 12, and is also rotatably mounted about theaxis of beam 12 as indicated by the arcuate arrow C.

Referring now to FIG. 2, a holographic apparatus is shown which includesthis invention, indicated within the dotted lines. This apparatusincludes, in addition to the above described beam splitter and half-waveplates, a coherent light source 24 from which the incident light 8radiates. The emergent light beam 12 becomes the object beam for theholographic apparatus and is reflected from a suitable reflector 26,directed through a beam expander 28, and through an object transparency30, then onto a hologram plate 32. Emergent beam 10 becomes thereference beam for this holography apparatus and is directed throughanother beam expander 28 and onto hologram plate 32 where it establishesand records the pattern of interference with the object beam 12.

This holography arrangement is more fully described in applicantsco-pending application Ser. No. 144,762, filed concurrently herewith.

In the use of this invention, as described with reference to FIG. 1 andas used for example in a combination as shown in FIG. 2, an incidentbeam of light may be divided into two components. These components arevariable as to intensity and their intensity ratio is likewise variable.The emergent beams, normally mutually perpendicularly polarized, areeach variable as to their azimuth of polarization, and likewise therelative difference of the azimuth of polarization of the two beams isvariable.

It may occur to others to make modifications of this invention whichwill lie within its concept and scope and not constitute a departure.Accordingly, it is intended that the invention be not limited by any ofthe details of its description but only by the following claims.

What is claimed is:

I. A light beam splitter capable of providing two light beams ofdifferent intensities, including, in optical alignment:

a birefringent medium,

azimuth control means to vary the azimuth of polarization of lightincident on said birefringent medium,

said birefringent medium effective to divide light incident thereon intotwo emergent beams,

plate rotatable about the axis of propagation of the light incident onsaid birefringent medium,

said beam splitter further including a half-wave retardation platedisposed in the path of, and rotatable about the axis of propagation of,one of said emergent beams to control the azimuth of polarizationthereof. 4. A light beam splitter as defined in claim 3 in which saidbirefringent medium is rotatable about the axis of propagation of thelight incident thereon.

1. A light beam splitter capable of providing two light beams ofdifferent intensities, including, in optical alignment: a birefringentmedium, azimuth control means to vary the azimuth of polarization oflight incident on said birefringent medium, said birefringent mediumeffective to divide light incident thereon into two emergent beams, saidazimuth control means effective to obtain varying intensities of saidemergent beams by controlling the azimuth of polarization of theincident light.
 2. A light beam splitter as defined in claim 1 furtherincluding: a half-wave retardation plate disposed in the path of, androtatable about the axis of propagation of, one of said emergent beamsto control the azimuth of polarization thereof.
 3. A light beam splitteras defined in claim 1 in which said azimuth control means is a half-waveretardation plate rotatable about the axis of propagation of the lightincident on said birefringent medium, said beam splitter furtherincluding a half-wave retardation plate disposed in the path of, androtatable about the axis of propagation of, one of said emergent beamsto control the azimuth of polarization thereof.
 4. A light beam splitteras defined in claim 3 in which said birefringent medium is rotatableabout the axis of propagation of the light incident thereon.